Reservoir Characterization of Mid Main Carbonate (MMC) Interval in Cipadati Field (North West Java Basin, Indonesia) to Support Detailed Reservoir Zonation

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T1S2_O4

Reservoir Characterization of Mid Main Carbonate (MMC) interval in Cipadati Field (North West Java Basin, Indonesia) to Support Detailed Reservoir Zonation

Winardi, S.1, Toha, B.1, Suryono, S.S.1, Prasetya, I. 2

1

Dept of Geological Eng-UGM, Jl. Grafika No 2, Yogyakarta-55281, Indonesia (winards@yahoo.com)

2

PT. Pertamina EP, Jl. Prof. Dr. Satrio No. 164, Jakarta Selatan-12950, Indonesia

Generally the MMC is known as a carbonate build up interval in the North West Java Basin, Indonesia, which contains hydrocarbons in some fields such as Rengasdengklok and North Cilamaya. In the Cipadati Field the MMC was drilled by the Explo#1 well and had a thickness of 79 meters. Previously the MMC was assumed to be a homogeneous carbonate reservoir, so petrophysical values gained from the Explo#1 well were used as default values along the entire interval. Further characterization of the MMC is needed to gain a deeper understanding of the heterogeneity of the reservoir including depositional stages, geometry, vertical facies changes, secondary pore types and porosity value. These parameters provided petrophysicists with the information necessary to divide the MMC reservoir into more detailed reservoir zones.

The most reliable data to characterize the reservoir is core data, however core is non-continuous through the interval so image logs were used as support data in the non-cored intervals. Well calibration was done using image logs, especially in combination with core, thin sections, cuttings and other log data. Lithological texture could be observed within the image logs, so, based on Dunham limestone classification the

lithofacies was identified. Seismic facies analysis, supported by well data, was also conducted to reveal the development of carbonate stages and their geometry during the formation of the MMC. The high resolution of the image log tool provided detailed observation of porosity types greater than 2.5 mm. The reservoir zonation was done based on lithofacies, pore types and porosity value.

The result of characterization shows that MMC is not a continuous single homogeneous carbonate but formed in 12 depositional stages. Externally the geometry of the MMC is of a carbonate buildup (classified as a skeletal mound carbonate), but internally the geometry of each stage varies from mound to sheet drape. Overall the MMC was deposited onto the shelf platform. The MMC in this area does not represent a reef build up. Various lithofacies are found ie alternation between wackstone and packstone in lower part and some shale interruption near the top of the interval. Secondary pore types which are observed along interval are vugular (isolated vugs, interconnected vugs, channeling vugs) and fracture porosity (open fracture and partially mineral filled fracture). The result of porosity calculation shows a variation between 5 and 19 percent. Based on its characteristic the reservoir can be divided into 19 zones (11 reservoir zones and 8 non-reservoir zones).

Acknowledgements

!

"

By :

Winardi, S.

1

_{Toha, B.}

1

_{, Suryono, S.S.}

1

_{, Prasetya, I.}

2

1

_{Dept of Geological Eng-UGM, Jl. Grafika No 2, Yogyakarta-55281, Indonesia}

2

_{PT. Pertamina EP, Jl. Prof. Dr. Satrio No. 164, Jakarta Selatan-12950, Indonesia}

winards@yahoo.com

September 2013

Outline

Geological Background

Data & Analysis

Result & Discussion

Geological Background

3

(After TT Jabarut 1998 vide Pertamina, 2005)

BP study team, 1996

CIPADATI

MMC

MMC

MMC in Explo#1 well was assumed to be a single

homogeneous reservoir.

Previously, petrophysic analysis used

single/same parameter for whole interval.

All tested intervals of MMC were water bearing.

EXPLO#1

Carbonate build up (eq MMC) distribution in Rengasdengklok high (Pertamina, 2005)

(Pertamina, 2005)

Data & Analysis

FMI log data from Explo#1

well at MMC interval

(1444-1523 m depth).

Composite log

data (GR, SP

,

Resistivity, Density

&

Neutron

).

Petrophysic analysis from

previous study.

Cutting description log

Conventional core description

at 1454.71-1461.3 m depth

intervals.

14 samples of

side wall core

description.

5 thin section descriptions.

8 seismic lines across

Cipadati field.

Other wells data around study

area.

Result-1: Reservoir characteristic (Facies, Pore types,

Features of subaerial exposure & Depositional stages)

7

Image display of wackestone and packstone facies.

packstone

wackestone

Distribution of vertical facies unit of MMC in Explo#1

NO.

DEPTH (m)

THIKCNESS (m)

FACIES

1

1444 - 1455

11

Wackestone

2

1455 - 1456

1

Serpih

3

1456 – 1460,3

4,3

Packstone

4

1460,3 - 1460,7

0,4

Serpih

5

1460,7 - 1462,5

1,8

Packstone

6

1462,5 - 1462,7

0,2

Serpih

7

1462,7 - 1496.3

33,6

Packstone

8

1496.3 - 1501,8

5,5

Wackestone

9

1501,8 – 1510,5

8,7

Packstone

10

1510,5 – 1515,3

4,8

Wackestone

11

1515,3 – 1518,5

3,2

Packstone

12

1518,5 - 1523

4,5

Wackestone

₉

11

fracture

vug

Feature of subaerial exposure

4 subaerial exposures are identified along MMC interval, at 1471.3, 1486, 1495, and 1507.8 m depth. High GR reading which is caused by the presence of paleosoil (filled secondary pore), as indicator of subaerial exposure.

Depositional Stages & Lateral Distribution

Result-2: Detailed Reservoir Zonation

15 POROSITY

TYPES

1 1444 - 1453.50 9.5 Wackestone Interconnected vug 2 1453.5 - 1457.00 3.5 non-reservoar

-3 1457 - 1458.00 1.0 Packstone Open fracture + interconnected vugs 4 1458 - 1466.00 8.0 non-reservoar

-5 1466 - 1468.00 2.0 Packstone Open fracture + channeling vugs 6 1468 - 1471.30 3.3 non-reservoar

-7 1471.3 - 1480.00 8.7 Packstone Interconnected vug 8 1480 - 1486.00 6.0 non-reservoar -9 1486 - 1493.50 7.5 Packstone Channeling vug 10 1493.5 - 1495.00 1.5 non-reservoar

-11 1495 - 1495.60 0.6 Packstone Partially interconnected vug 12 1495.6 - 1498.00 2.4 non-reservoar

-13 1498 - 1499.00 1.0 Wackestone Partly mineral filled fracture + vugs 14 1499 - 1507.80 8.8 non-reservoar

-15 1507.8 - 1509.00 1.2 Packstone Interconnected vug 16 1509 - 1510.50 1.5 Packstone Primer-intergranular 17 1510.5 - 1511.00 0.5 Wackestone Interconnected vug 18 1511 - 1515.00 4.0 Wackestone Open/partially healed fracture + vugs 19 1515 - 1523.00 8.0 non-reservoar

-ZONES DEPTH (m) THICKNESS (m) FACIES

Relation between porosity types and

cementation factor (m) equations

Vugular & fossilmoldic porosity, use Nugent (1984)

Vugular & oomoldic porosity, use Nurmi(1984)

Cementation factor (m) of reservoir zones of MMC in Explo#1

NO DEPTH (m) THICKNESS (m)

Re-calculation result of Water Saturation (Sw) of MMC in Explo#1

1 1444 - 1453.50 9.5 0.12 1.46 1.5 0.07 0.99

CONCLUSIONS

1.

General reservoir characteristic of MMC in Cipadati Field:

Consist of some lithofacies of wackestone, packstone and shales.

Had some subaerial exposures, found at 1471.3, 1486, 1495 and 1507.8 m

depth.

MMC was formed in12 depositional stages and stage 1, 6, 10, 12 are penetrated

by Explo#1 well.

Both of intergranular primary porosity and secondary porosity types such as

vugular (isolated vugs, interconnected vugs, channeling vugs), fractures (open

fracture, partially mineral filled/healed fracture) are observed. Some dual

porosity of fractures-vugs system also found.

2.

MMC is not a single homogeneous reservoir, it consists of nineteen

(19) different characteristic zones. Eleven (11) zones are reservoir and

eight (8) of them are non-reservoir zones.

19

CONCLUSIONS

3.

Reservoir petrophysic properties of MMC;

The thickest reservoir is zone 1 at 1444-1453.5 m depth with 9.5 m thick and the

thinnest one is zone 6 at1495-1495.6 m depth with 0.6 m thick.

Highest porosity interval is zone 6 at 1495-1495.6 m depth (average PhiE 19 %) and

the lowest porosity interval is zone 9 (1509-1510.5 m depth) and zone 10

(1510.5-1511 m depth) with average PhiE of both is just 5 %.

The highest value of cementaion factor (m) is 2.59 found at packstone facies in zone

6 and the lowest one is 1.31 found at wackestone facies in zone 10.